Ribonuclease in different chromosomal species of the mole rat, superspecies Spalax ehrenbergi: concentration in the pancreas and primary structure.

ABSTRACT

Ribonucleases are found in considerable quantities in the pancreas of a number of mammalian taxa and a few reptiles. The ribonuclease content varies greatly in different species. Large quantities are found in ruminants and species that have a ruminant-like digestion and in a number of species with coecal digestion. This is a response to the necessity of digesting large amounts of RNA derived from the microflora of the stomach of ruminants or species with ruminant-like digestion or of the coecum of species with coecal digestion. The amino acid sequence of pancreatic ribonuclease from the chromosomal species 2n = 60 of the mole rat, superspecies Spalax Ehrenbergi was determined. From the comparison of the sequence with those of other mammalian species we found that Spalax diverged from the myomorph rodent branch before the divergence of the Muridae (mouse, rat) from the Cricetidae (hamster, muskrat). Spalax ribonuclease shares several amino acid residues with other myomorph rodent species. These are not or only rarely observed outside this rodent suborder. Although the ribonuclease content varies greatly in different mammalian species, the variation in content between individuals within a species is small. Spalax is an exception to this with ribonuclease contents varying over more than an order of magnitude in different individuals. Ribonucleases isolated from the chromosomal species 2n = 52, 2n = 58 and 2n = 60 have identical elution positions on reversed-phase HPLC. The enzyme from the 2n = 54 species, however, elutes at a slightly earlier elution position. No amino acid sequence differences have been found hitherto between the ribonucleases of the four chromosomal species of Spalax ehrenbergi occurring in Israel. However, due to lack of material we were unable to determine more than about 20% of the sequence of the enzyme from the 2n = 54 species, which is the oldest offshoot.